Could someone look at this and see if it appears to be corrupted? I’m troubleshooting an iMac that was working fine and then there was a series of power outages and afterwards the iMac does not POST. Diagnostic LED #1 and #2 are illuminated, but not #3. I did a quick visual inspection of the logic board and found no visibly bad/burned components and found no shorts. The lack of Diagnostic LED#3 officially means “logic board unable to communicate with GPU”, but if the computer wasn’t POSTing due to a corrupt BIOS, it would behave like this as well.
I thought it could be a corrupt BIOS. Looking at my dump in UEFITool, the parser indicates that there may be some corruption, but I honestly don’t know enough about BIOS editing/repairing or UEFITool to interpret the parser output, but the wording certainly makes it sound like something isn’t right.
I’m attaching a dump of my original BIOS which I suspect is corrupt as well as a supposedly clean BIOS I found online for this model and finally, a screenshot of the parser output in UEFITool.
First of all, please dont flash anything from web… this is Apple iMac not a PC bios.
You should get in to Macrumors forum with this issue for more user experienced opinions.
Theres UEFI tools for Mac here: Releases · LongSoft/UEFITool (github.com)
I really dont know how well this tool performs on Apple roms/smc and it should be compared against an official Apple FW rom update, that can extracted from pkg’s, but the development of this tool have many Apple users contribution, thats why my opinion is to search within Mac forums.
Good luck
Modern Apple FW updates are not standalone anymore, they’re inside the new (only supported macOS) OS pkg update and must be extracted…i really dont remember anymore how it was, i dont have new Macs only 3 old 2008 machines and all maxed out…its been a while since i touched Apple fw…
But theres info about this is Macrumors
Thank you both for the advice and also for suggesting Macrumors. I have created a thread there. In the meantime, I am researching extracting the firmware from the macOS update package. Found a lot of seemingly good info, but it will take some time for me to study it. Thank you again.
